In recent years, in order to suppress global warming, reduction of carbon dioxide emissions into the atmosphere has been required. In particular, carbon dioxide (CO2) emissions attributable to coal-fired power generation account for nearly 30% of worldwide CO2 emissions, and reduction of carbon dioxide emissions from coal-fired power generation can be expected to have a large effect as a strategy for mitigation of global warming. One of technologies for separating, recovering and storing carbon dioxide (carbon capture and storage) (hereinafter, sometimes referred to as “CCS” herein) employs a recovery method using a chemical adsorption method, and plays an important role in reduction of the amount of carbon dioxide in boiler combustion exhaust gases in thermal power plants etc.
Typical CCS technology may include the following techniques. A combustion exhaust gas from a boiler is subjected to treatments such as denitration, dust collection and desulfurization as necessary, and then introduced into an absorption and regeneration tower, and the combustion exhaust gas and an absorbent liquid are brought into contact with each other in the absorption and regeneration tower. Accordingly, CO2 in the combustion exhaust gas is absorbed into the absorbent liquid to remove CO2 from the combustion exhaust gas. The absorbent liquid having absorbed CO2 is heated by, for example, a hear exchanging device, and guided into the regeneration tower, and CO2 is dissociated from the absorbent liquid in the regeneration tower, so that CO2 is recovered. On the other hand, the absorbent liquid, from which CO2 has been dissociated in the regeneration tower, is recycled to the above-mentioned absorption and regeneration tower, and reused for absorption of CO2 in a combustion exhaust gas. As absorbent liquids to be used in such a CCS technology, many absorbent liquids containing amine and water have been investigated.
However, a large amount of energy is required to heat the whole amount of an absorbent liquid to 100° C. or higher in release of CO2, and thus there arise problems in terms of CO2 recovery efficiency and profitability. In addition, since the amine aqueous solution generates a large amount of degradation products such as amine derivatives, organic acids and amino acids due to long-term use, and thus causes a reduction in efficiency, it is necessary to periodically remove impurities or replace the absorbent liquid. As a method for recovering carbon dioxide in a gas, a plurality of kinds of methods have been known heretofore. Currently, a variety of methods are widely known. For example, a method in which carbon dioxide-containing gas is brought into contact with an alkanolamine aqueous solution in an absorption and regeneration tower to absorb carbon dioxide, the carbon dioxide recovery aqueous solution is then heated, and carbon dioxide is desorbed and recovered in a releasing tower was developed in the first half of the 1900s, and has been practically used since then. Here, examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine and the like are known, but usually monoethanolamine is used. However, when an aqueous solution of such an alkanolamine is used as an absorbent liquid, a degraded product of the amine corrodes the device, and therefore it is necessary to use expensive corrosion-resistant steel for the device, Further, in order to improve absorbed carbon dioxide desorption performance, the desorption temperature is increased, and thus there arises a problem that degradation of the amine is accelerated. There is also a disadvantage that much energy is needed for recovering carbon dioxide from the absorbent liquid due to the influence of water.